Process for producing dibasic carboxylic acids



March 17, 1959 E. l. CROWLEY ETAL PROCESS FOR PRODUCING DIBASIC CARBOXYLIC ACIDS Filed May 3, 1955 NORMAN w. FRANKE, RALPH w. HELWIG THE R 4717 80 5) U ites! that? Pe ice.

first ,sta ge of our 'process can be conducted satisfac tofily either a't atmospheric or elevated pressures. While? i i pressures as highas about 1000 pounds per'square inch l gauge can be employed without afiecting adversely the oxidation reaction, we prefer to employ pressures ranging Edgar I. Crowlemllttsburgh, Norman W. Franke, Penn from about atmospheric to about150 poundsper'square I Township, 'Anegnenyi County, hndRhlph W. Helwig, inch gauge. The temperature of the airoxidationlre Oakmont, Pa., assignors to Gulf Research & De p: action is not critical and can be varied over a. great}: 9 ttsb alp a acg p ra c h arange. Thus. a temperature of about 100, to about; t h I 1 10 400 C. is satisfactory, although a temperature of aboutj A li ti M '1955, serial 505, 02 150 to about 1901C. is preferred. In order to cut 1 down on the nitric acid consumption in thesecond stage. 1 260-452) of our process, the saturated aliphatic hydrocarbon should) i C y be oxidized for a time sufiicient to obtain an ai'roxidaa This inveritionrel'a'tes to an oxidation process forcontion product having a saponification number above'aboutf verting saturatedaliphatic hydrocarboiis to organic acids 100, and preferably about 150 to about 450. While the f and more particularly'an oxidation process for contime required to obtain an air oxidation product hav ihg vertmg saturated aliphaiiehydrocarbons to dibasic carthe desired saponification number is, of course, depend boxylic acids. g y ent upon a number of variables, a period of about}. Saturated aliphatic hydrocarbons, such as parafiin wax, to about 20 hours is generally sufficient. The amount can be oxidized with nitric acid under controlled conof molecular oxygen required to obtain the air oxidation. ditions to produce a product comprising dibasiccar- Product is not Critical an extless isjllesifaliltt,will;v boxylic acids. The amount of oxidant generally needed though about 0.5 gram to about 2.0 grams of oxygen in such a process to obtain satisfactory yields of dibasi c per gram of chargeishsufiicient. y f carboxylic acidsis unusually high, and methods have ahOXidatiOh Product Cihtainhd i h S therefore been sought to increa e the yield of dibasic .or a fraction thereof is thereafter passed to a second carboxylic acids for the same a unt of itric id stage where itis oxidized with nitric acid. While'the employed. One method of reducing the consumption of A amount of nitric acid employed in the nitric acid stage nitric acid involves preoxidi zing the charge stock corni n t critical n n bevaried v ra lw d r g prising a saturated aliphatic hydrocarbon with, air and Provided shlhciehtlileid F e F fhr the'dsivfed oxidafw thereafter subjecting at least a portion of the oxidation lion, charging ahhht to hhoht 20 Pa of h' acid product obtainedto further oxidation with nitric acid. P P of Oxidation P C Q tothe nitric i Further reduction in they consumption of nitric acid t on. zone i lsu i e t c the de i d a e involves employing reaction conditions in the nitric acid H cafhhxrylhl ac'ids- 1 i reaction stage that? permits most effective use of the h pr re in heuit ic acid reactionzone issimik oxidants available in said st I ,larly not critical and can be varied over a wide range,

We have found that the oxidation of saturated aliphatic a P r of about atmospheric to ahhht 15.00 PoundS hydrocarbons can beimproved and the amount ofdibasic P Square h gauge vbeing P f F best, u ts carboxylic acids produced therefrom can be .increased we Operate theihhric acid hh a pe h of by a process which comprises oxidizing a composition 40 O P ab tl 0 P er y ht p ra consisting essentially of saturated aliphatic hydrocarbons a o 75 y r i. C- Th I he m with air or other gas'containingmolecular oxygen, subthe Sal-mated. aliphatic y c in .the n r d jecting at least a part of thesoxidation: product obtained; heeessalY t substantial amounts hh h a to further oxidation with nitric acid to obtain a mixture boxylic fiel var e inversely with th icomprising a nitricacid: phase and an oil phase, washing 145 ehahlple, ut h n m amount 9 reaction. is i t i said oil phase with water,;and thereafter recovering" dih e bei t 3 as a n y basic cal-bonus mivdsfmm gaidnitric acid phase in less than about two hours at 130 C. The reaction said Water wash. a 1 r can be carried outat a constant temperature or the Saturated aliphatiq hydrocarb n -b ili about temperaturecan be varied with time. Thus, the reaction, 250 F. and having about eight or more carbon atoms. 50 h h started a elewtttemperathre h and h mixm h f b' .gmployed as charge Stock, temperature gradually raised toya selected maximum, for the production of dibasic acids in accordance with temperature the as h he hiseohhhhed i our process, although, forease of operation, we prefer the. hh h l h h isreaehed: the ireaehehw to employ saturated aliphatic hydrocarbons having from eah he meihteihed at the selected maximum lh about 10 to about 40 carbon atoms; 'Included among for the desired length ofhlhei i the saturated aliphatic hydrocarbons which can be em Durihg thethxideheh of the hQ -P h i$ 0 ployed in our process are petroleum waxes, parafiinic oils, saturated a s hydrocarbons with hithie heid, the foots oil, oils and waxes. obtained from the Fischer acid b down t0 form 2 NO, N2 r e h Tropsch process, no ctane, decane, cetane, etc. While some which Additionalmisrepresent lhe h we prefer to employ charge stocks consisting of satue reaction Zone h result of theyoxidahoh i h r rated aliphatic hydrocarbons welcan also employ charge aID-Q XIdiZflI products of saturated aliphatic hydrocarbons stocks which are predominantly saturated aliphatic hyf of course Since an aqueous Solution of i e h drocarbons and which can contain cycloparaflins. Such 1s employed some water is introduced into the h' 1 charge stocks can be prepared from a variety of types aeld reaehoh Zone with the aeid- N 2 e- 'Fh hh of crude oils. When the crude oil is essentially parafiinic, 204, which i in equilibrium with 2- 2: as ehi the charge may be recovered by distillation but where the as 2 4 has been found he an excellent oxidizing r d il i of a mixed type, various combinations f agent for air-oxidized products of saturated aliphatic. treatments can be employed ,to obtain the charge, such hydrosatbons- Thereforeiif the nitric acid heaehoh t eas distillation and solvent extraction, distillation and Seeehd stage (from P e is wfiducted h w crystallization, or chromatographic separation. taihel Suchrthai 2 formed during the Process s' p 'h -it yented from escapingNO ilI react with the air-oxidized;

Oxidation of saturated aliphatic hydrocarbons with! products of saturated aliphatic hydrocarbons in the nitric air or other gas containing molecular oxygen in the acid reactor. In addition, in the absence of substantial amounts of oxygen in the nitric acid reactor, NO formed will react with N to form N 0 which is also believed to be an excellent oxidizing agent for air-oxidized products of saturated aliphatic hydrocarbons. At the same time, N0 and N 0 will react with the water present to form nitrous as well as nitric acid, both of which are believed to beexcellent oxidizing agents for the purpose of this invention. In this way, by utilizing N0 NO, water, other nitrogen oxides and nitrogen acids formed during the process as oxidants, the amount of nitric acid necessary in thesecond stage of our process for convertin'g air-oxidized products of saturated aliphatic hydrocarbons to dibasic acids is substantially reduced.

In order to cut down on the amount of nitric acid consumed in the second stage of our process, gaseous oxygen can be added directly to the nitric acid reactor or evolved nitrogen oxides, except N 0, can be regenerated in a second vessel adjacent thereto. The amount of air or other gas containing molecular oxygen added to the nitric acid reactor or necessary to regenerate the nitrogen oxides is not critical and can be varied over a wide range, although we prefer to use more than the theoretical amount to insure adequate regeneration. For example, about 30 to about 100 grams of oxygen per 100 grams of air oxidation product of saturated aliphatic hydrocarbon and 500 grams of 70 percent nitric acid are sufiicient for purposes of regeneration or introduction into the nitric acid reaction zone.

When oxygen is introduced into the nitric acid reactor, a smaller amount of nitric acid is lost by conversion to nitrogen or N 0 than if no oxygen were introduced to the reactor. If the exhaust gases are passed to a separate vessel where the nitrogen oxides, except N 0, are regenerated with gaseous oxygen to higher oxides of nitrogen, nitrous acid and nitric acid, and these materials allowed to return to the nitric acid reactor, a substantial saving in the amount of nitric acid converted to nitrogen and N 0 is found. As stated, with no substantial amounts of oxygen in the nitric acid reactor, NO, N0 as Well as N 0 are formed and these are passed to the regenerator. N0 remains unaffected by the presence of oxygen but NO and N 0 are regenerated by the oxygen to N0 The N0 already present, as well as the N0 formed in the regenerator, is condensed therein and recycled to the nitric acid reactor where the N0 reacts with the airoxidized products of saturated aliphatic hydrocarbons as such or is converted by reaction with water to nitric acid. In the regenerator the N0 can combine with water to form nitric acid which is recycled to the nitric acid reactor.

At the end of the nitric acid reaction the oxidation product obtained comprises an upper oil-phase layer and a lower nitric acid layer. The upper oil-phase layer can vary from about 5 to about 50 percent by weight (based on the air oxidation charge) and usually comprises a mixture of C to C dibasic carboxylic acids and C to C monobasic carboxylic acids. The nitricacid layer contains unreacted nitric acid as well as dibasic carboxylic acids'having from 3 to about 12 carbon atoms. We have found that the amount of dibasic carboxylic acids recovered in the two stage oxidation of saturated aliphatic hydrocarbons can be further increased by washing the oil-phase layer with water and thereafter additionally recovering dibasic carboxylic acids from said water Wash.

In carrying out the washing step, the oil-phase layer is separated from the nitric acid layer and is washed with at least one-half times and preferably about one to about 2 times its volume of water. The wash water containing the water soluble constituents of the oil-phase layer, including the mixture of C to C dibasic carboxylic acids, is thereafter combined with the mixture of be present. The water washing is effective for several reasons. It succeeds in removing the water-soluble acids, including dibasic carboxylic" acids, from the oil-phase layer. In addition, the Wash water is then used in stripping nitric acid from the organic acids present in the nitric acid layer. Moreover, it permits the major proportion of Water-soluble acids extracted fromthe oil phase by water washing to be purified together in the same recovery system.

A method of carrying out our invention employing a first stage air oxidation, a second stage nitric acid oxidation, wherein the second stage of the process is conducted in a closed container and the nitrogen oxides formed therein are regenerated in a separate regenerator and recycled to the second stage of the process, and the step of washing a portion of the oxidation product obtained in the nitric acid reactor is illustrated in the single drawing which describes a flow diagram of such typical procedure. For simplicity, valves, gauges, etc., not needed for an understanding of the invention have been omitted. The drawing is hereby incorporatedin and made a part of the present specification.

A saturated aliphatic hydrocarbon is charged into oxidation reactor 2 by line 4 and a gas containing molecular oxygen such as air by line 6. The saturated aliphatic hydrocarbon is vigorously agitated at an elevated temperature in reactor 2 for a time sufficient to obtain an oxidation product having a saponification number above about 100 and preferably about 150 to about 450. In order to facilitate the oxidation in reactor 2, a catalyst such as vanadium pentoxide can be employed. Volatilized lower molecular weight products produced during the air oxidation step are removed overhead from reactor 2 and passed to condenser 8 by line 10. The condenser is preferably maintained at a temperature of about 35 to about 90 F. by any suitable means, although any temperature sufficient to condense a large part of the volatilized lower molecular Weight products can be employed. The condensed lower molecular weight products in condenser 8 resolve themselves into two phases, an upper organic phase comprising oxidized hydrocarbons, including lower organic acids, esters and aldehydes, and a lower aqueous phase comprising formic, acetic and propionic acids, and are removed from condenser 8 by line 12. Uncondensed lower molecular weight products comprising excess air, nitrogen, carbon monoxide and carbon dioxide are re moved from condenser 8 by line 14.

The air oxidation product is removed from reactor 2 by line 16 and passed to nitric acid reactor 18, and nitric dibasic carboxylic acids of the nitric acid layer and the resulting mixture is then subjected to distillation toremove therefrom water and any nitric acid which may acid is led to reactor 18 by line 20. The pressure in reactor 18 is maintained at an elevated pressure. The nitric acid reactor can be a stainless steel pressure vessel equipped with a stirrer, and in the instant embodiment, is provided with a nitrogen oxide regenerator 22. The air oxidation product and nitric acid are heated in reactor 18, by means not shown, and stirred. If desired, reactor 18 can be operated continuously, in which case a coil-type reactor or one vessel or a number of vessels in series can be employed. Nitrogen oxides formed during the process are removed overhead from reactor 18 by line 24 and passed to nitrogen oxides regenerator 22. A controlled amount of air or other gas containing molecular oxygen is introduced in the regenerator by line 26 and, as noted, N 0 and NO are regenerated therein to N0 which, along with the N0 already present, is condensed therein and recycled by line 28 to reactor 18. The pressure in regenerator 22 is of the same order as that existing in reactor 18 and the temperature is sufficiently low, from about 0 to about 120 F., preferably about 20 to F, so as to enable the N0 in the gases to condense and be returned to reactor 18. N N 0, CO and CO as well as oxygen-containingregenerating gas, are removed overhead from regenerator 22 by line 30.

After sufiicient residence time in reactor 18, the oxidation product is removed from the reactor by line 32 n p sed t epa ator-- 4whichiism i ingdtalifi-i fimm Pe -att r p ab ut 3110 .abea 1:10 atet rab. nahoum Nita-a o t 90 R where para e in oaa pn r oil-= phase layer and a lower nitric acid layen The upper, ilr s lay v y romaabo t noabout 5.0psr- 5 e t se e a -a idati n. product charg d; to. reactor 18), and usually comprises. an igrture of Q io, C dibasic and C to C r nonobasie carboxylic aeids,.,. he ilip la e s emo ed rom separa rfi lthy. line; an passed o a wash rfitfi. Wate is odn edi 1 a h 3 ou e wa i i ately .mixe tw th... he. a l-pha e er t e ein-U Wa hin it at. he lfliicp aa avsrawd no hes tate in single s hu c n b carried out in aplurality of stages, The resultingmixs ture in washer38 resolves itself into two phases, an upper oil-phase, substantially ,tree of water-soluble acids, which can be recycled by 1ine42 to either air. oridationreactor 2, nitric acid reactor 18yor,both, and. the water wash which is removed by line 4.4 and passed to eyapor aton lfis The n ic a d a lis smqv dt o ep r tor 34hr line.4,8,and passedto vacuum still 50. Nitric acid, is removed .overhead from vacuum still 50 by, line 52 and. can t be sent to an absorption tower, where thenitric acid can be reconcentrated with fresh N0 and air, or can be sent to a distillation zone where it oan-be .reconcentratedxby distillation. The temperature and pressuregin vacuum i still 50 ar e notcritical and. can 'vary from a,temperature of about 80 to about 200.F. and a pressure of about" 0.5 to about 20 inches of mercury, r 1f desired, nitric acid soobtained and so reconcentratedcanybe recycled toline 20for use in reactor 18, 1

The residue from vacuum still 50, comprising a slurry of solid and liquid acids, is removed from the still by line 54 and passed to evaporator 46 where it is combined withwashpvater entering through line 442" The'evaporator is'maintained at a suitable temperature, about 100 to about 230911 1, and a suitable pressure, about 0.5 to about 29 iriches of mercury, effective to remove from the mixture therein substantially all of the water andthe nitric acid not previously removed in vacuum' stil1"50and 40 present with the dibasic carboxylic acids in the evapo-.- rator. The mixture of water andnitric acid is removed overhead from evaporator 46 through line56 and discharged. Instead ofemployingboth ava'cuuih' Istill and'jan evaporator 46 in the procedure abo.v,.we:;can pass both the nitric acid phase and. the .washmwaternin n line 44 to a single unit wherein the nitric acid and the at an. b tsm vsd r s ts ls ist lla sa rgrepr ff ld r s1 v ha then t isas q Phase a bined with "e- T wash. water? and: the .who'le sub eote d-,to r distillation, or ,evapo t the. nitric @ciq, phase .can. t 0 v oldistill ation or eyaporati ceGl ITES Qafter which the; residue {can be c sameunit with wash waterand .theresu 1n can be, treated to remove w ter and nit c acid therefromp The; es e i mJ or es 46 sq t s ns. slu of s li J and l qui acids i .rs svsd; ths tr m .bn l n 58 aiid passed to cooler 60. Thepslurry is, cooled in cooler 60 to .a suitable; low temperature, preferabiy to. a; temperatureofabout to about F. andallowed 60 to. nd. theses-$ Pe mit thes s a z t pn .ot he d basicacigls present,. I t -12 L The minture of dibasi rboxyiic. acids tobtarned in q stfih: m r si tCs o C10 dib sis a s ca e. i used as such or can be subjected to further treatment, Thus, the mixture can be discharged from cooler .60 through line 62 and passed to filter 64. The filtratefrom this filtration step is removed byline 66 andpassed to line- 68. and. after suificient filter cake has rforrned in filter:64, filtration is stopped and the cake; iswashed with benzene .frornaline 70. If desired, ,the mixture of dibasic carboxylic .acids obtained in cooler 60 can: be slurried withtone toaboutSJparts of benzene and. the slurryqthen filtered. The .filter cake can thereafter be washed with benzenew-The benzene washings are 're 'fi 74. Benzene is removed overhead from stripper .74 and recycled by line 76, and that remaining from the benzene washings not going overhead in line 74 is passed to line 68. The filter cake, after: the benzene washings, is

transferred to dryer 78. by conveyor line. 80. r In dryer 78;,any,.benzene'present-inithe filter cake is removed overhead by line 82 and recycled to line 70 by means i has a preferential attraction for any .monobasic acids present, such as diethyl ether, ethylpropyl ether, di-

propyl ether, dimethyl etber,'.benzene, carbon tetrachloride, ethyl carbonate, chloroformf' t'richloroethylene, etc., through line 86, and the resulting solution is passed upwardly it into the base of'extraction: chamber 88. We

have found that diethyl etheris especially effective in our process, and our discussion will be with reference to it. .Waterior dilute aqueous solution of a mineral acid such as hydrochloric acid, nitric acid, etc., is introduced into the top of chamber 88 by line 90 and is mixed "therein with the solution. enteringfromline 68 resulting in a lower aqueous phase and an upper ether phase.

The aqueous phase is removed from the base of chamber 88 by line 92 and passed to stripper 94. 'Water is stripped from .the aqueousphase in stripper 94 and re- 1 moved overhead. by line 96; while a mixture comprising aliphatic dibasic carboxylic acids'isremovedby line 98.

Water in. line 96ris passedto separator 100, wherein water is removed. by line 102 and any ether which may have been carriedby the water is removed by: line 104 aridre 'cycledtoline 86. q

The .ether. phase isremo'ved overhead from chamber 88 by line 106 andpassed to stripperlOS, whereinether isremoved by line 110 and recycledto'line 86 by line 104.:and a :complex mixture comprisinghigher'dibasic carboxylic acids, monobasic acids and nitrogen contain-j ing acids is removed by line 112." If desired, the acids removed in line 112 can be recycled to either air oxida tion reactor- 2, nitric acid reactor 18, or both.- t The product obtained in line 84 comprises a mixture of aliphatic dibasic carboxylic. acids containing from about 4 to about 10 carbon atoms, predominantly acids having an.even.ntimber of carbon atoms; and the product obtained in line .98comprises a mixture of aliphatic clibasic acids containing about 3 to about 9carbon atoms per 0 molecule, predominantly acids having an odd number of carbon atoms.

Thefollowing examples illustrate the increased yields obtained by carrying Rout the two-stage oxidation of saturated aliphatic hydrocarbons in accordance with our invention. 1

EXAMPLE I r 500 grams of Gulfwax (a refined paraflin wax having a melting point of 133 F.) was oxidized in air at .a temperature of 160 C. by blowing therethrough 2.5 liters of air per minute per kilogram of wax and 475 grams of an oxidation product having a saponification number of 221 was obtained. Into a continuous autoclave was fed the 475 grams of air oxidation product,

a 1412 grams of 65 percent aqueous nitric acid and 315 grams of oxygen. The pressure was maintained at about 500=pounds per square inch gauge, the temperature at C. and the contact time was 30 minutes. The produetpbtained comprised a two-phase liquid product con 1 0 sistlng of 1406.8 grams of nitric acid phase and 223.9

grams of oil phase. The oil phase was washed three 7 an openbeaker over a water bath to evaporate dissolved water yielding 185.3 grams of oil phase acids.

The nitric acid phase was divided into two equal por-' tions which were separately worked up in the following manner identically except that with portion A the oil phase washings were employed as the following described nitric acid chasers while with portion B similar volumes of fresh water were used as chasers.

The nitric acid phase was placed in a distillation flask and nitric acid distilled off at a pot temperature of 35 to 45 C., the temperature being regulated by the degree of vacuum maintained on the system, the pressure being adjusted around 30 mm. Hg. Near the end of the distillation as the pot temperature began to increase, the pressure was gradually lowered to about mm. Hg and the temperature was then permitted to increase to 50 C. at which point the distillation was stopped. In portion A" the first oil phase wash was added to the residue in the still pot and distillation was resumed under conditions similar to the main distillation. Distillation was again stopped at a pot temperature of 50 C. at 5 mm. Hg. This constituted the first nitric acid chaser. Similarly the second and third oil phase washes were added and dis tilled off. In portion -B the nitric acid chasers consisted of three 150 ml. portions of distilled water. The final residue of crude dibasic acids remaining in the pot was weighed, transferred to a beaker, and intimately contacted with two-thirds its weight of benzene. The resulting slurry was filtered and the precipitate returned to the beaker and rewashed with same quantity of benzene and again filtered. This procedure was repeated once more. After the final filtration, the precipitate was spread on paper and the residual benzene permitted to evaporate to the air. The dried solids were weighed as precipitated acids. The benzene filtrates were combined and placed over a water bath until substantially all of the benzene had evaporated leaving a wash oil which was dissolved in 3 ml. ether per gram of oil and the resulting solution was extracted three times each with a volume of water equal to the volume of ether used to dissolve the wash oil. The water was then evaporated from the aqueous extract phases and the ether from the rafiinate phase yielding extracted acids and raffinate acids, respectively. The following table indicates the yields of products obtained, the figures being parts per hundred parts of airoxidized wax charged to the nitric acid stage. Correction has been made for the fact that oil phase washings from the total oil phase were used in working up only one half of the nitric acid phase.

EXAMPLE II 861.5 grams of an oxidized wax mixture consisting of 322.5 grams of oil phase acids recovered from a previous nitric acid stage oxidation of air oxidized deoiled foots oil and 539.3 grams of a 234 saponification number air M oxidized deoiled foots oil obtained by blowing 576 grams of deoiled foots oil for eleven hours at 160 C. with 2.5 liters of air per minute per kilogram of wax were continuously passed to a continuous autoclave together with 2530 grams of 6 5 .6 percent aqueous nitric acid and 2140 liters (standard temperature and pressure) of air. The

pressure was maintained at about 500 pounds per square inch gauge, the temperature at 130 C. and the contact time was 30 minutes.

Products from this nitric acid stage oxidation were worked up in a fashion similar to that of the previous example. In this example isopropyl ether was employed in working upthe crude DBA (Distillation Residue) rather than benzene and ether as in the previous example. In this instance isopropyl ether was used to wash the crude acids three times, each time with a weight of isopropyl ether equal to one-third the weight of the original crude acids. The combined isopropyl ether filtrates were then extracted with water three times each time using a weight of water equal to the weight of the combined filtrates. The nitric acid phase was divided into two equal portions and each worked up separately and in the same manner except that with one portion the aqueous washings of the oil phase were used as nitric acid chasers while with the second portion fresh water was used as nitric acid chasers. In this run 433 grams of oil phase was re covered and washed three times, each with 200 ml. of water at about C. Separation of the aqueous washes resulted in recovery of 222.4, 176.0, and 166.1 grams of oil phase washes half of which were used in turn as the 1st, 2nd, and 3rd chasers in the one case. Identical quantities of distilled Water were used as the chasers in the other case.

The product yields (part per parts of oxidized wax charged to the nitric acid stage) for these procedures were calculated as indicated below inTable II.

The increased yields of dibasic earboxylic acids obtained by the simple expediency of washing the oil phase layer obtained in the nitric acid reactor with water and further treating the water washings obtained is shown in each of the tables. In Table I, the yield of the purified dibasic acid fraction was increased by 6.7 percent, while in Table II the increase in yield amounted to 8.2 percent. The rafiinate acids obtained in the process are a mixture of dibasic and nitrogen-containing organic acids which can be employed as such as chemical intermediates. In Table I the increase in yield of rafiinate acids amounted to 12.8 percent, while in Table II the increase amounted to 12.3 percent.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claim.

We claim:

A process for the production of dibasic carboxylic acids from a charge stock consisting essentially of saturated aliphatic hydrocarbons boiling above about 250 F. and having at least 8 carbon atoms which comprises subjecting the charge stock to oxidation with a gas containing molecular oxygen for a time sufficient to obtain a product having a saponification number above about 100 but below about 450, subjecting said product to further oxidation at an elevated temperature with nitric 9 10 acid to obtain a product comprising a nitric acid phase References Cited in the file of this patent containing nitric acid and dibasic carboxylic acids and an oil phase carrying dissolved dibasic carboxylic acids, sep- UNITED STATES PATENTS arating said nitric acid phase and said oil phase, washing 2,009,664 James July 30, 1935 said oil phase with water, removing unreacted nitric acid 5 2,439,513 Hamblet et a1. Apr. 13, 1948 from said nitric acid phase to obtain a product containing 2,452,741 Fleming Nov. 2, 1948, dibasic carboxylic acids, combining said latter product 2,486,454 Zellner Nov. 1, 1949 and said water wash, removing water and additional nitric 2,653,962 Mitchell et a1 Sept. 29, 1953 acid from the resulting mixture, and thereafter recovering 2,662,908 Logan Dec. 15, 1953 dibasic carboxylic acids from the resulting mixture. 16 2,771,482 Brown et al Nov. 20, 1956 

